Monday, August 31, 2009

Aptina revealed its BSI plans, but only in Chinese and Japanese versions of Tech-On. We, English readers, seem to be out of luck. Google translation is not particularly interesting, other than saying that BSI will shine at 1.1um pixel pitch and that Aptina plans to launch BSI products by the fall of 2010. (see the full text at the end of this post). However, the figures in the article show the logic behind Aptina BSI plans.

The first figure compares Aptina FSI with competitors BSI at 1.4um node:

Another figure shows Aptina QE simulation of 1.1um pixels. Color crosstalk looks to me on the high side, but Aptina still has a lot of time to improve till the product launch:

Next figure shows a cross-section of 1.75um BSI prototype. The silicon thickness appears to be about 1.5um - thinner than Omnivision and Sony, which probably has some red QE implications. I hope Aptina will improve on this too:

Finally, below is Google translation of Chinese version of Tech-On article, for what it is worth:

"U.S. Aptina Imaging Corp. Is, CMOS high sensitivity sensor technology BSI (back irradiation) announced plans to apply. BSI is a Sony and the U.S. OmniVision Technologies, Inc. Is a technology that uses a series of major manufacturers such as image sensors. CMOS sensor is a leading manufacturer in Aptina plan did not become clear introduction.

The BSI, CMOS can be eliminated and the disadvantage of low sensitivity and only Ieta image sensor (NIKKEI MICRODEVICES posted a feature article in the September 2009 issue). In principle, CCD high sensitivity can be compared to the sensor. The introduction of Sony's digital video and digital cameras already seems to have become popular among users of its quality when shooting at night.

BSI using the technology, the structure can be achieved without decreasing the image sensors capture light. Generally the CMOS sensor, the sensor element at the top of the about three-layer metal wiring layer. Screening the light incident from an angle, especially in this metal wiring layer, reduce the sensitivity was. Therefore, BSI sensor in the bottom of the device (back) has been to adopt a light. From the back of the substrate to form a MEMS sensor devices and processing technology by cutting a thin, light guide.

Aptina is U.S. Micron Technology, Inc. Is independent from the image sensor manufacturers. Micron Technology has its own era, "Light Guide" by, Aptina use of the BSI for the foreseeable future and had no view. Light guide is a technology to guide the light sensor element of the metal wiring layers from top to bottom. Customers can also reach the light sensor element from the diagonal. Using this technology, a pixel pitch of 1.4μm and BSI does not until you do not have to reduce the sensitivity of technology (Figure 1).

However, the 1.1μm pixel pitch will to fully demonstrate their will to prevent the effect of the light guide, BSI technology and need. This will greatly improve the sensitivity and S / N ratio can be improved (Figure 2). From this perspective, Aptina is the pitch 1.1μm CMOS sensor BSI plans to introduce the technology. When production is the prospect that the fall of 2010 years. The company is, BSI technology to 1.75μm and 1.4μm pitch pitch prototype device has been already applied (Figure 3-6)." (Links to Fig 4, Fig 5 and Fig 6.)

This report only indicates that Aptina will apply the BSI on 1.1um pixel pitch, because Aptina has its own "light guide" technology which can imporve the "shading" due to the metal layers on 1.4um pixel pitch. Aptina believes that without BSI, the 1.4um pixel can still have enough sensitivity.

To prove the BSI, Aptina already has some test chips based on 1.75um and 1.40um pixel pitch.

Thus, ST, Aptina and Toshiba will apply the BSI for 1.1um pixel. Sony has different thinking, and it applied the BSI on 1.4um for its owned camcorder. (in fact, there should be 2 teams developing the image sensor inside Sony - Sony LSI and Sony Broadcast)

About 2 years behind OVT, well, I believe that Micron already has lots of patents related to BSI far than 2 years ago. Maybe some people from Micron can point it out.

> Sony has different thinking, and it applied the BSI on 1.4um for its owned camcorder.

So far Sony camcorders use 1.75um BSI pixel (or 1.77um, according to other sources). Omnivision applies BSI for 1.4um pixel.

> To prove the BSI, Aptina already has some test chips based on 1.75um and 1.40um pixel pitch.

As an afterthought, this can explain just 1.5um silicon layer thickness in Aptina BSI sensors - may be they optimized it for 1.1um pixel, even though the prototype has 1.75um pitch. To me it looks strange that Aptina does not use 1.1um in the prototype, as the photodiode implants are very different between 1.75um and 1.1um BSI.

Front-side technology can theoretically beat BSI technology. Think about it. With BSI, photodiode implants must be brought to back-side silicon surface (for all colors), or lose red, green, and blue q.e. Front-side can have appropriate depths of photodiode for each different color channel, while BSI cannot. It becomes a huge problem for BSI compared to when FSI is done correctly, as both the size, depth, and width of a photodiode will impact cross-talk and thermal generated shot noise in low light conditions. Grinding the back-side of a wafer and bringing all colors down to surface is not the ideal situation. I think Aptina knows what they are doing, they have number one market share and are always thinking one step ahead.